The present invention relates to a method of copy protecting optical discs, and to optical discs when so protected. The invention also extends to a method of preventing the mastering of optical discs by non-enabled encoders.
Optical discs, such as the various formats of compact discs (CDs), and of digital versatile discs (DVDs) are increasingly used for carrying information for many different applications. The information encoded onto the optical discs is generally very valuable, and accordingly, they are increasingly copied by counterfeiters. Furthermore, recordable CDs are now available and CD writers for writing the information content from one disc to such recordable discs are now readily available to the domestic consumer. This means that new and effective methods for copy protecting the optical discs are required.
There is described, for example, in WO98/57413 a method of providing an optical disc with an authenticating signature. This authenticating signature is arranged so that it is not, or cannot be, copied by available machines for reading and writing data from CDs. For example, in WO98/57413, a sector of a CD is provided with a pattern of errors which cannot be corrected by the error correcting rules and thereby constitutes an uncorrectable sector or “bad sector” on the disc. The existence of the expected bad sector is taken as an authenticating signature and is used to identify a genuine disc.